As you can see, there's a part of the island you can't reach, because we all know rocks and ocean are impassable terrain, right?
|Who is that?|
Piece of cake. Of course you could give this spot more complex logic, and using this construct would be a great way to flag an area as visited. You could have a quest giver order the player to visit a shrine, which is only reachable by crossing an area like this, then use the invisible actor to flag the site as visited. Hmm. That's a good idea actually... off to tinker!
I hope this and the other posts like it have been useful, thanks for reading!